Yosry Ahmed <yosryahmed@xxxxxxxxxx> writes: > On Sun, Jun 18, 2023 at 7:00 PM Huang, Ying <ying.huang@xxxxxxxxx> wrote: >> >> Hi, Yosry, >> >> Yosry Ahmed <yosryahmed@xxxxxxxxxx> writes: >> >> > This reverts commit c3096e6782b733158bf34f6bbb4567808d4e0740. >> > >> > That commit made sure we immediately add the new page to the LRU before >> > remove_migration_ptes() is called in migrate_move_folio() (used to be >> > __unmap_and_move() back then), such that the rmap walk will rebuild the >> > correct mlock_count for the page again. This was needed because the >> > mlock_count was lost when the page is isolated. This is no longer the >> > case since mlock_count no longer overlays page->lru. >> > >> > Revert the commit (the code was foliated afterward the commit, so the >> > revert is updated as such). >> > >> > Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx> >> > --- >> > mm/migrate.c | 24 +++++++++--------------- >> > 1 file changed, 9 insertions(+), 15 deletions(-) >> > >> > diff --git a/mm/migrate.c b/mm/migrate.c >> > index 01cac26a3127..68f693731865 100644 >> > --- a/mm/migrate.c >> > +++ b/mm/migrate.c >> > @@ -1279,19 +1279,6 @@ static int migrate_folio_move(free_page_t put_new_page, unsigned long private, >> > if (unlikely(!is_lru)) >> > goto out_unlock_both; >> >> The patch itself looks good to me! Thanks! >> >> Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx> > > Thanks for taking a look! > >> >> And, it seems that we can remove the above 2 lines and "out_unlock_both" >> label now. That can make the code simpler a little. Right? > > I am not familiar with this code. If we remove the above condition > then pages that have is_lru == 0 (i.e __PageMovable(src) is true) and > page_was_mapped == 1 will call remove_migration_ptes(). This wouldn't > happen without removing the above 2 lines. If this combination is > impossible (is_lru == 0 && page_was_mapped == 1), then yeah we can > remove the above condition. > > It looks like __SetPageMovable() is only called by zsmalloc, z3fold, > and balloon_page_insert(). The former 2 will never have those pages > mapped into userspace. I am not familiar with balloon_page_insert(), > but my gut feeling is that those are pages used by the driver and are > also not mapped into userspace. You can take a look at migrate_folio_unmap(), where "page_was_mapped" will not be set to 1 if !is_lru. Best Regards, Huang, Ying > So I guess we can just remove the condition, but a confirmation for > the above would be reassuring :) > >> >> Best Regards, >> Huang, Ying >> >> > - /* >> > - * When successful, push dst to LRU immediately: so that if it >> > - * turns out to be an mlocked page, remove_migration_ptes() will >> > - * automatically build up the correct dst->mlock_count for it. >> > - * >> > - * We would like to do something similar for the old page, when >> > - * unsuccessful, and other cases when a page has been temporarily >> > - * isolated from the unevictable LRU: but this case is the easiest. >> > - */ >> > - folio_add_lru(dst); >> > - if (page_was_mapped) >> > - lru_add_drain(); >> > - >> > if (page_was_mapped) >> > remove_migration_ptes(src, dst, false); >> > >> > @@ -1301,9 +1288,16 @@ static int migrate_folio_move(free_page_t put_new_page, unsigned long private, >> > /* >> > * If migration is successful, decrease refcount of dst, >> > * which will not free the page because new page owner increased >> > - * refcounter. >> > + * refcounter. As well, if it is LRU folio, add the folio to LRU >> > + * list in here. Use the old state of the isolated source folio to >> > + * determine if we migrated a LRU folio. dst was already unlocked >> > + * and possibly modified by its owner - don't rely on the folio >> > + * state. >> > */ >> > - folio_put(dst); >> > + if (unlikely(!is_lru)) >> > + folio_put(dst); >> > + else >> > + folio_putback_lru(dst); >> > >> > /* >> > * A folio that has been migrated has all references removed >>
